In situ polymerization of monomers in the presence of a catalyst is a process frequently used in the preparation of polymers. In this process, for instance, polymerizable monomers are added to a catalyst-containing solution. This process is often used in the preparation of an intrinsically conducting polymer.
A process for the in situ preparation of an intrinsically conducting polymer is described in U.S. Pat. No. 4,617,353. In that process, a matrix polymer is dissolved in a liquid solvent. This solvent also contains a suitable catalyst. Subsequently, a polymerizable monomer is added to that solution, upon which this monomer polymerizes to form an intrinsically conducting polymer.
Although it is in principle suited for the in situ preparation of a polymer, the process mentioned in U.S. Pat. No. 4,617,353 presents a number of practical problems. The catalyst is present in the solution, and as a consequence the polymerization reaction commences immediately after the addition of the monomer. Thus, a polymer is obtained instantaneously. In order subsequently to give form to the polymer, or to a blend thereof, a (number of) processing step(s) is required. This instantaneous polymerization reaction is .not desirable if one or more further processing steps are necessary, because the prepared polymer, or a blend hereof with other polymers, is very hard to process or cannot be processed at all.
The intrinsically conducting polymers mentioned in U.S. Pat. No. 4,617,353 are very hard to process or cannot be processed at all. Consequently, it is quite difficult to shape or mould compounds containing such intrinsically conducting polymers to obtain products having intrinsically conducting properties.
A process for producing an electrically conductive article is disclosed in Europe 314311. In this process monomers present in the polymer composition are polymerized to yield a conjugated polymer, would be desirable to stretch the polymer's composition or during the polymerization step to obtain good mechanical properties. However, as a practical matter, it is not readily possible to conduct that process as described wherein those two process steps are simultaneously carried out. The reason is the fast rate of the polymerization reaction of the monomers. At the temperatures prevailing during the stretching step, the polymerization reaction proceeds instantaneously. In view of the relatively long time which is needed for the stretching step, it is impossible to allow the two processes to proceed simultaneously over a prolonged period. In general, in the known process, the polymerization reaction is already complete while the major part of the stretching step has yet to take place. In practice, the bulk of the stretching step is takes place after polymerization of the monomers. As a result the desired combination of properties is not obtained. Thus, it is not possible to produce an article which has both good mechanical properties and good electrically conducting properties by the abovementioned process.
Another process is disclosed in Synthetic Metals, 4: 217-221 (1988). According to the process as there described, pyrrole monomers are polymerized in the presence of a catalyst to yield the electrically conducting polypyrrole polymer. During the polymerization, the release of protons leads to incorporation of an amount of 2,5-bis-(2-pyrrolyl)pyrrolidine (BPP) in the polypyrrole. This gives rise to a significant reduction of the electrically conducting properties. To largely avoid the undesirable incorporation of the BPP impurity in polypyrrole, polymerization must occur in a reaction mixture that is pH buffered, in such a manner that the pH is greater than 1 but lower than 7. To this end a buffer is added to the reaction mixture. This results in a significant improvement of the electrically conducting properties of the electrically conducting polymer that is obtained.
Although the process described in Synthetic Metals is suitable for the preparation of an electrically conducting polymer with good electrically conducting properties, it has major disadvantages. The polymerization reaction of the monomer units is immediately initiated in the presence of a catalyst. As a result, an electrically conducting polymer is directly obtained, which is precipitated as a powder in the reaction mixture. The precipitate thus formed is not suitable for thermoplastic processing and is not or hardly capable of being shaped into a coherent moulding compound .